Large dielectric constant, high acceptor density, and deep electron traps in perovskite solar cell material CsGeI3
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Materials Science & Technology Division and Center for Radiation Detection Materials and Systems
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Materials Science & Technology Division and Center for Radiation Detection Materials and Systems; Beihang Univ., Beijing (China). School of Physics and Nuclear Energy Engineering
Here we report that many metal halides that contain cations with the ns2 electronic configuration have recently been discovered as high-performance optoelectronic materials. In particular, solar cells based on lead halide perovskites have shown great promise as evidenced by the rapid increase of the power conversion efficiency. In this paper, we show density functional theory calculations of electronic structure and dielectric and defect properties of CsGeI3 (a lead-free halide perovskite material). The potential of CsGeI3 as a solar cell material is assessed based on its intrinsic properties. We find anomalously large Born effective charges and a large static dielectric constant dominated by lattice polarization, which should reduce carrier scattering, trapping, and recombination by screening charged defects and impurities. Defect calculations show that CsGeI3 is a p-type semiconductor and its hole density can be modified by varying the chemical potentials of the constituent elements. Despite the reduction of long-range Coulomb attraction by strong screening, the iodine vacancy in CsGeI3 is found to be a deep electron trap due to the short-range potential, i.e., strong Ge–Ge covalent bonding, which should limit electron transport efficiency in p-type CsGeI3. This is in contrast to the shallow iodine vacancies found in several Pb and Sn halide perovskites (e.g., CH3NH3PbI3, CH3NH3SnI3, and CsSnI3). The low-hole-density CsGeI3 may be a useful solar absorber material but the presence of the low-energy deep iodine vacancy may significantly reduce the open circuit voltage of the solar cell. Still, on the other hand, CsGeI3 may be used as an efficient hole transport material in solar cells due to its small hole effective mass, the absence of low-energy deep hole traps, and the favorable band offset with solar absorber materials such as dye molecules and CH3NH3PbI3.
- Research Organization:
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC)
- Grant/Contract Number:
- AC05-00OR22725
- OSTI ID:
- 1328304
- Journal Information:
- Journal of Materials Chemistry. A, Vol. 4, Issue 36; ISSN 2050-7488
- Publisher:
- Royal Society of ChemistryCopyright Statement
- Country of Publication:
- United States
- Language:
- English
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